Balloons in Stanton Tunnel

Intrigued, the obvious answer was yes, especially as RIDC Melton is located close to the company’s base in Nottingham. But why on earth did Hitachi want to put balloons in a tunnel? Was it some sort of celebration?

The Melton facility

RIDC Melton is the new name for the Old Dalby test track near Melton Mowbray – Network Rail has two Rail Innovation and Development Centres, the other being RIDC Tuxford (formerly High Marnham) in North Nottinghamshire. The line was originally built as a twin-track railway connecting Melton Mowbray to Nottingham – the Manton route – which allowed express trains from London to the North to bypass Leicester and avoid a turnback at Nottingham.

The new route opened in 1879 and finally closed in 1968. However, British Rail retained the line from Melton Mowbray to Edwalton as a test track for the Advanced Passenger Train. Since then, Class 390 Pendolino trains, London Underground S Stock and Hitachi’s new Class 800/801 Intercity Express Programme (IEP) trains have all been tested there.

One track runs for 13 miles between Melton Mowbray and Edwalton, is fitted with the new Series 1 25kV overhead catenary, and is cleared for 125mph running. The other, from Old Dalby to the entrance to Stanton tunnel, is just four miles in length, has London Underground-style four-rail DC electrification, and is currently testing trains and signalling for LU’s 4LM (four lines modernisation) programme on behalf of Thales and Bombardier.

Stanton tunnel is 1,330 yards in length and one of four tunnels on the line. Currently, only the Down line is in use as part of the longer, high speed test track on which Hitachi is testing its IEP trains that are destined for deployment on the West Coast and Great Western main lines. As part of the IEP train acceptance regime, there was a requirement to fulfil aerodynamic and pressure pulse testing in a tunnel that didn’t have any ventilation shafts, up to a maximum train speed of 125mph.

Unfortunately, the test track does not have any tunnels of sufficient length without shafts. So the novel solution devised by Hitachi engineers was to temporarily fit inflatable balloons inside the tunnel’s three ventilation shafts. It seemed simple enough in principle; however, in practice, as with many innovative ideas, it proved more challenging than first thought.

Bridgeway would be working with Hitachi and track operator Serco to develop a solution.

Preparation

Given the busy nature of the IEP test programme, good planning was essential and all three parties collaborated to provide different elements of the scheme, with support from plant partners TXM.

Firstly, all three shaft eyes had to be prepared prior to the arrival of the balloons. This included removal of all existing launders and brackets and grinding flush the holding bolts. The bottom two metres of each shaft also had to be cleaned of over 70 years of soot, deposited by passing steam trains. All this was necessary to ensure that the balloons had an airtight fit within the shaft eye and would not be punctured during the fitment of the balloons or whilst train testing was in progress.

In order to ensure that the balloons could remain stable within the shafts during the tests, metal brackets, eye bolts and fabric ratchet straps needed to be fitted around the base of the shaft eye, after all detritus had been removed, and at the top of the shaft so that the balloon would be in tension and couldn’t move.

With the need to work on both the top and bottom of the shafts at the same time, two entirely different access methods were employed. The team used an RRV MEWP to access the shaft eye from track level and Bridgeway’s roped access team descended from the ‘pepper pots’ at the top of the tunnel shaft to fit chain blocks and steel lifting cables. These would be used to raise the deflated balloons into the shaft eye and provide stability when the balloon was fully inflated.

In total, six threaded-bar eye bolts were drilled and fixed using chemical resin anchors around the circumference of each of the three shaft eyes, and four bespoke fabricated metal brackets fitted in the same manner to the tunnel crown outside the shaft eye on both longitudinal and transverse axis.

These were required both to locate the balloon within the shaft and to affix the restraint straps diagonally across the base of the shaft, to prevent the balloon from falling into the tunnel during inflation and provide vertical restraint during the testing programme.

The balloons were specially manufactured in reinforced rubber and delivered to Asfordby depot at RIDC Melton. They were already fitted with metal D-rings at the top to which the chain block would be fitted, and with an airline connector at the bottom centre for inflation purposes.

Fitment

At this point the balloons were placed trackside and chain blocks hoisted the balloons into the shafts, guided both by Bridgeway abseilers and by staff on the MEWP platform to ensure that the precious cargo wasn’t damaged during the process. Care had to be taken while manoeuvring the balloons around the OLE wires which were still in place, although de-energised, and ran directly under the ventilation shafts.

Adjustments needed to be made to centralise each balloon and the restraint straps were tightened to the crown brackets, securing the balloon. At this point the ratchet straps placed across the eye were fitted and tightened to prevent the balloon from falling onto the track during inflation. Finally, the chain block at the shaft top was adjusted by the abseilers to tension the balloon.

Inflation

With the balloons now fitted into the shafts, the tricky process of ensuring that they could be inflated needed to be tackled. Three large-capacity air compressors and associated hoses were transported into the tunnel by RRV, lifted onto the redundant track bed of the former Up line and fixed into position. The hoses were then resin anchored to the tunnel haunches and crown brickwork and connected to the balloon air connector and reducer valve within the shafts, ready for inflation.

Due to the nature of the rubber balloons, their inflation had to be regulated and they were continually adjusted to ensure that they remained central in their shafts and to guard against external damage as the balloon touched the shaft brickwork. Finally, when all the three balloons were inflated to the correct pressure, a final check for leaks was made before being handed over to Hitachi for IEP testing to begin.

In order for the aerodynamic tests to be valid, the balloons had to retain their pressure throughout. This meant that they all had to be inflated on the same night shift followed by aerodynamic testing the following day. On subsequent testing days, the balloons were checked prior to testing and any minor pressure loss was rectified.

Testing

Once the balloons had been fitted, Hitachi engineers installed the necessary test equipment. This included the placement of anemometers and pressure sensors both outside and inside of the tunnel and on-board the IEP test train itself. Results would be analysed and to prove that the train – not to mention the tunnel lining and shafts – could withstand the inflicted air pressure differentials. The novel balloon system worked and the IEP test programme produced positive results. IEP trains are now continuing their testing programme away from RIDC Melton on the East Coast and Great Western main lines.

The fixtures and fittings have been retained within the shafts at Stanton tunnel so the system can be used for future testing of other high-speed trains. In one small way, Bridgeway has assisted the introduction of Hitachi’s Class 800 and 801 trains, heralding the next stage in high speed train development in Britain.